1. Field of the Invention
The field of the invention relates generally to conveyor belt systems, and more specifically to devices employed for maintaining the alignment of endless conveyor belts on a conveyor system, such as those conveyor systems used in the mining, food and package handling industries.
2. Statement of the Art
A typical conveyor system includes a support frame having an upper load carrying portion and a lower return portion. The frame supports a plurality of idler rollers that are configured to carry an endless belt. Material is conveyed on the upper load carrying portion of the conveyor system, while the endless belt is returned along the lower return portion.
Uneven loading, worn or misaligned rollers, or other components of the conveyor system that are out of alignment or imbalanced may cause the belt to wander in a transverse direction relative to the center of the conveyor system. Such misalignment of the belt can result in significant and expensive repairs of the conveyor belt if not quickly corrected. Specifically, with conventional conveyor systems, when the belt wanders to one side, the edge of the belt may be allowed to contact and rub against components of the frame of the conveyor system. If the belt is allowed to scrape against a stationary object such a component of the frame, the belt will become quickly damaged. Such wear along an edge of the belt can result in, for example, delamination of the layers of material comprising the belt and significant removal of material along the edge of the belt.
Replacement of prematurely worn or damaged belts is a relatively expensive procedure both in the man hours required to replace such a belt as well as the expense of the belt itself. In addition, because of the typical long length of such belts, the belt must be removed and replaced in sections. Thus, in order to replace a section, workers must cut and remove the damaged section of belt and splice in a new belt section of the same length. Because of the weight alone of such a belt section, multiple workers must be employed to perform the replacement operation. Additionally, such a section of belt may cost between $1,000 and 50,000.
Devices for maintaining the alignment of continuous belt conveyor systems have been known for decades. For example, in U.S. Pat. No. 3,913,729 to Andrews, a belt aligner comprises a pair of hourglass shaped rollers that can move in a direction transverse to the direction of belt movement in order to force the belt into alignment. The rollers are designed to receive the edge of the belt within a circumscribing channel. One problem known in the industry with such rollers is the tendency for the belt to ride out and over the roller when the belt edge of the belt or the roller itself becomes worn or when debris passes between the roller and the edge of the belt.
Similar problems exist with the devices shown in U.S. Pat. No. 2,609,084 to Hersey and U.S. Pat. No. 3,278,002 to Robins, the belt can easily ride up and over the roller. Furthermore, devices, such as that shown by Robins, require complex systems to operate. Robins requires a separate hydraulic system to be installed in conjunction with the conveyor system. Additionally, Hersey requires a pivoting subassembly to allow the entire belt support structure to pivot in order to encourage proper alignment of the belt. Thus, such prior art systems require significant retrofitting to existing conveyor belt systems or installation of completely new conveyor systems in order to obtain the claimed benefits of such belt training devices.
Accordingly, it would be advantageous to provide a belt alignment device for use on both existing continuous belt conveyor systems and newly constructed belt conveyor systems that is relatively easy and inexpensive to manufacture, can be easily installed on existing conveyor systems, and provides significantly better belt alignment than other devices known in the art.
In accordance with the present invention, a conveyor belt alignment device is provided which comprises an idler roller rotatably attached to a mounting bracket. The idler roller has a first substantially cylindrical portion extending over an upper surface of the conveyor belt proximate the edge of the belt and a second substantially cylindrical portion having a diameter greater than the first cylindrical portion abutting against the edge of the conveyor belt. For a given conveyor system, a plurality of idler rollers are attached to the conveyor system over the rollers which support the endless conveyor belt. That is, the belt is effectively sandwiched between the idler rollers and the support rollers of the conveyor system.
Preferably, the idler rollers are rotatably mounted to the mounting bracket with an elongate axle extending through the idler roller. The axle comprises an elongate shaft having a first externally threaded end, a second externally threaded end and a central non-threaded portion. The non-threaded portion has a length greater than a longitudinal length of the idler roller and a diameter that prevents the threaded fasteners from advancing beyond the threads of the shaft. As such, when the idler roller is attached to the elongate shaft, the idler roller can freely rotate relative to the shaft even when the threaded fasteners are fully engaged upon the shaft.
Because a portion of the idler roller of the present invention rides on top of the endless belt of a conveyor system, debris will necessarily pass between the belt and the roller. In order to accommodate such debris while minimizing damage to the belt, as may be the case if the roller were rigidly held against the belt, the idler roller is provided with a biasing device, such as a coil spring, to allow movement of the idler roller away from the belt (i.e., in a direction substantially perpendicular to a plane defined by an upper surface of the belt). As such, the idler roller forces the belt against its respective carrying roller in order to hold and maintain the belt in proper alignment.
In a preferred embodiment, a mounting arm is attached proximate a first end thereof to a conveyor system and has a second end extending to proximate an edge of the conveyor belt. An L-shaped mounting bracket attaches the idler roller to the mounting arm. A biasing device is coupled between the mounting arm and the mounting bracket for biasing the idler roller toward an upper surface of the conveyor belt.
In yet another preferred embodiment, the idler roller is comprised of a cylindrically shaped wheel having a first portion with a first diameter for riding upon the upper surface of the belt and a second portion for abutting against the edge of a belt of a conveyor system. In addition, the difference between the first diameter and the second diameter is less than a thickness of the conveyor belt. As such, the second portion is prevented from contacting the carrying roller which would cause undesirable wear of the carrying roller.
In yet another preferred embodiment, the first and second portions of the idler roller comprise an integral wheel. The wheel is provided with an axle for rotatably mounting the wheel to a mounting bracket. In addition, the axle further defines an elongate bore extending at least partially through the axle for providing a pathway for grease to be applied between the wheel and the axle.
In still another preferred embodiment, the first portion of an idler roller mechanism comprises a first roller configured for extending over and rolling against an upper surface of the conveyor belt proximate an edge thereof, and a second roller oriented approximately ninety degrees from the first roller and configured for rolling against the edge of the conveyor belt. Preferably, the second roller is spaced below the first roller a distance less than a thickness of the conveyor belt so that the second roller does not contact the carrying roller when in operation.
When the belt training idler rollers of the present invention are used in conjunction with a belt conveyor system, such as the belt conveyor systems disclosed in U.S. Pat. Nos. 2,399,913 to Dodge, U.S. Pat. No. 2,488,859 to Garbed, U.S. Pat. No. 2,561,641 to Thomson, U.S. Pat. No. 2,609,084 to Hersey, U.S. Pat. No. 2,743,004 to Wright, U.S. Pat. No. 3,278,002 to Robins, and U.S. Pat. No. 4,351,431 to Benton, Jr. et al. each herein incorporated by this reference as well as other belt conveyor systems known in the art, a plurality of such belt training idler rollers are attached at various points along the path of the belt. More specifically, when the belt conveyor system includes a support structure, a plurality of carrying idler rollers coupled to the support structure for supporting a feed path of the endless conveyor belt, and a plurality of return idler rollers coupled to the support structure supporting a return path of the endless conveyor belt, a plurality of belt training rollers are coupled to the support structure proximate an edge of the endless conveyor belt and are positioned above each of the carrying idler rollers. The belt training rollers are configured to compress a portion of the endless conveyor belt proximate an edge thereof between the belt training rollers and the carrying idler rollers. In addition, a plurality of belt training rollers are coupled to the support structure proximate an edge of the endless conveyor belt above each of the return idler rollers in a manner similar to the belt training rollers attached relative to the carrying rollers.